As an inspection technique for a fine shape of a substrate surface, a method of detecting scattered light by irradiating a laser beam has been known. However, in this method, only a foreign substance having a certain size and anomaly such as a missing pattern can be detected.
Also, a method of scanning a sample by an optical microscope with high resolution at a high speed has been known. However, in this method, it is difficult to detect a defect whose size is equal to or smaller than a resolution (0.61λ/NA, λ: light wavelength and NA: numerical aperture (<1) of an objective lens) determined by the light wavelength. Although a fine defect whose size is smaller than 200 nm which is a half of a wavelength of visible light has been handled by, for example, using an expensive deep ultraviolet optical system or others, it is extremely difficult to handle a pattern such as smaller than 100 nm.
More particularly, a defect such as a pattern positional shift is more difficult to appear as image brightness and darkness than a defect such as a lost pattern, an excessive pattern, and adhesion of a foreign substance, and therefore, it is extremely difficult to detect the defect.
Accordingly, conventionally, an inspection method of scanning a substrate by electron beam having high resolution has been known. However, in this method, there are problems that it is difficult to inspect the entire surface of the substrate in realistic time because a scanning speed is too slow, and that normal electron microscopic images cannot be obtained because a substrate having no conductivity such as a quartz substrate is charged due to the use of the electron beam.
Also, Japanese Patent Application Laid-Open Publication No. 2008-82999 (Patent Document 1) discloses an inspection method with fine resolution and without depending on light resolution by detecting the scattered light from a pattern on a substrate when a head approaches the substrate to scan in a state that fine near-field light smaller than light resolution is generated by using a plasmon-enhanced head.